Human reproduction is
sexual reproduction
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote th ...
that results in
human fertilization
Human fertilization is the union of a human egg and sperm, occurring primarily in the ampulla of the fallopian tube. The result of this union leads to the production of a fertilized egg called a zygote, initiating embryonic development. Scient ...
to produce a human offspring. It typically involves
sexual intercourse between a
sexually mature
Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definiti ...
human
male
Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization.
A male organism cannot reproduce sexually without access to ...
and
female
Female ( symbol: ♀) is the sex of an organism that produces the large non-motile ova (egg cells), the type of gamete (sex cell) that fuses with the male gamete during sexual reproduction.
A female has larger gametes than a male. Females ...
.
During sexual intercourse, the interaction between the
male
Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization.
A male organism cannot reproduce sexually without access to ...
and
female reproductive systems results in
fertilization
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
of the
ovum by the
sperm to form a zygote.
These specialized reproductive
cells are called
gamete
A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
s, which are created in a process called
gametogenesis
Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic di ...
.
While normal cells contain 46
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
s (23 pairs), gamete cells only contain 23 single chromosomes, and it is when these two cells merge into one
zygote
A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.
In multicell ...
cell that
genetic recombination occurs and the new zygote contains 23 chromosomes from each parent, giving it 46 chromosomes (23 pairs).
The zygote then undergoes a defined development process that is known as human embryogenesis, and this starts the typical 9-month
gestation period that is followed by
childbirth
Childbirth, also known as labour and delivery, is the ending of pregnancy where one or more babies exits the internal environment of the mother via vaginal delivery or caesarean section. In 2019, there were about 140.11 million births glob ...
.
The fertilization of the ovum may be achieved by
artificial insemination
Artificial insemination is the deliberate introduction of sperm into a female's cervix or uterine cavity for the purpose of achieving a pregnancy through in vivo fertilization by means other than sexual intercourse. It is a fertility treatment ...
methods, which do not involve sexual intercourse.
Assisted reproductive technology also exists.
Biological and legal requirements
In order for human reproduction to be achieved, an individual must have undergone
puberty
Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a bo ...
first, requiring
ovulation
Ovulation is the release of eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be fertilize ...
in females and the
spermarche
Spermarche—also known as semenarche—is the beginning of development of sperm in boys' testicles at puberty.''Adolescence and Emerging Adulthood: A Cultural Approach'', Jeffrey Jensen Arnett, N.J.: Prentice-Hall, 3rd edition, 2006. It is the c ...
in males to have occurred prior to engaging in
sexual intercourse or achieving
pregnancy
Pregnancy is the time during which one or more offspring develops (gestation, gestates) inside a woman, woman's uterus (womb). A multiple birth, multiple pregnancy involves more than one offspring, such as with twins.
Pregnancy usually occur ...
through non-penetrative means. Before puberty, humans are
infertile, as their genitals lack reproductive function (only being able to discharge
urine
Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra.
Cellular ...
).
Legal factors also play a vital role in the achievement of human reproduction: a
minor under the
age of consent cannot give legal consent to sexual intercourse or artificial alternatives to reproduction, the former case of which is liable to have the older party charged with
statutory rape
In common law jurisdictions, statutory rape is nonforcible sexual activity in which one of the individuals is below the age of consent (the age required to legally consent to the behavior). Although it usually refers to adults engaging in sexual ...
, depending on jurisdictions.
Even for minors above the age of consent,
comprehensive sex education
Comprehensive sexuality education (CSE) is a sex education instruction method based on-curriculum that aims to give students the knowledge, attitudes, skills, and values to make appropriate and healthy choices in their sexual lives. The intention i ...
advises both consenting parties to use
contraception
Birth control, also known as contraception, anticonception, and fertility control, is the use of methods or devices to prevent unwanted pregnancy. Birth control has been used since ancient times, but effective and safe methods of birth contr ...
to avoid both
sexually transmitted disease
Sexually transmitted infections (STIs), also referred to as sexually transmitted diseases (STDs) and the older term venereal diseases, are infections that are spread by sexual activity, especially vaginal intercourse, anal sex, and oral ...
s and
early, unplanned/unwanted pregnancies. Pregnancy in girls under the age of 15 is especially discouraged due to their reproductive systems having yet to reach full maturity.
Anatomy
Male reproductive system
The male reproductive system contains two main divisions: the
testes
A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...
where
sperm are produced, and the
penis
A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...
which discharges the sperm as
semen
Semen, also known as seminal fluid, is an organic bodily fluid created to contain spermatozoa. It is secreted by the gonads (sexual glands) and other sexual organs of male or hermaphroditic animals and can fertilize the female ovum. Sem ...
(this is known as an
ejaculation
Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential compone ...
). In humans, both of these organs are outside the
abdominal cavity. Having the testes outside the abdomen facilitates temperature regulation of the sperm, which require specific temperatures to survive about 2-3 °C less than the normal body temperature i.e. 37 °C. In particular, the extraperitoneal location of the testes may result in a 2-fold reduction in the heat-induced contribution to the spontaneous mutation rate in male germinal tissues compared to tissues at 37 °C. If the testicles remain too close to the body, it is likely that the increase in temperature will harm the spermatozoa formation, making conception more difficult. This is why the testes are carried in an external
scrotum
The scrotum or scrotal sac is an anatomical male reproductive structure located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum co ...
rather than within the abdomen; they normally remain slightly cooler than body temperature, facilitating sperm production.
Female reproductive system
The female reproductive system likewise contains two main divisions: the external genitalia and the internal genitalia.
The ovum meets with the
sperm cell: a sperm may penetrate and merge with the egg, fertilizing it with the help of certain hydrolytic enzymes present in the acrosome. The fertilization usually occurs in the
oviduct
The oviduct in mammals, is the passageway from an ovary. In human females this is more usually known as the Fallopian tube or uterine tube. The eggs travel along the oviduct. These eggs will either be fertilized by spermatozoa to become a zygote, o ...
s, but can happen in the uterus itself. The
zygote
A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.
In multicell ...
then becomes
implanted in the lining of the uterus, where it begins the processes of
embryogenesis and
morphogenesis
Morphogenesis (from the Greek ''morphê'' shape and ''genesis'' creation, literally "the generation of form") is the biological process that causes a cell, tissue or organism to develop its shape. It is one of three fundamental aspects of deve ...
. When the
fetus
A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...
is developed enough to survive outside of the
uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...
, the cervix dilates and contractions of the uterus propel it through the birth canal, which is the vagina, and thereby gives external life to the newborn
infant. This process is called
childbirth
Childbirth, also known as labour and delivery, is the ending of pregnancy where one or more babies exits the internal environment of the mother via vaginal delivery or caesarean section. In 2019, there were about 140.11 million births glob ...
.
The ova, which are the female sex cells, are much larger than the spermatozoon and are normally formed within the ovaries of the female fetus before birth. They are mostly fixed in location within the ovary until their transit to the uterus, and contain nutrients for the later
zygote
A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.
In multicell ...
and
embryo. Over a regular interval known as the
menstrual cycle, in response to hormonal signals, a process of
oogenesis matures one ovum which is released and sent down the Fallopian tube. If not fertilized, this egg is flushed out of the system through
menstruation.
Process of fertilization
![Biological life cycle of humans 2](https://upload.wikimedia.org/wikipedia/commons/7/7e/Biological_life_cycle_of_humans_2.png)
Human reproduction normally begins with copulation, though it may be achieved through
artificial insemination
Artificial insemination is the deliberate introduction of sperm into a female's cervix or uterine cavity for the purpose of achieving a pregnancy through in vivo fertilization by means other than sexual intercourse. It is a fertility treatment ...
, and is followed by nine months of pregnancy before childbirth. Pregnancy can be avoided with the use of contraceptives such as
condoms and
intrauterine devices.
Copulation
Human reproduction naturally takes place as
internal fertilization
Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female body. Internal fertilization, unlike its counterpart, external fertilization, brings more control to the female with reproduction. For inte ...
by sexual intercourse. During this process, the man inserts his erect
penis
A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...
into the woman's
vagina
In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
and then either partner initiates rhythmic
pelvic thrust
The pelvic thrust is the thrusting motion of the pelvic region, which is used for a variety of activities, such as dance or sexual activity.
Sexual activity
The pelvic thrust is used during copulation by many species of mammals, including hum ...
s until the male
ejaculate
Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential componen ...
s semen, which contains sperm, into the vaginal canal. The sperm and the ovum are known as the
gametes
A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
(each containing half the genetic information of the parent, created through
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately r ...
).
The sperm (being one of approximately 250 million sperm in a typical ejaculation) travels through the vagina and cervix into the uterus or Fallopian tubes. Only 1 in 14 million of the ejaculated sperm will reach the Fallopian tube. The egg simultaneously moves through the Fallopian tube away from the ovary. One of the sperm encounters, penetrates and fertilizes the ovum, creating a
zygote
A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.
In multicell ...
. Upon
fertilization
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
and
implantation, gestation of the fetus then occurs within the uterus.
Pregnancy rates for sexual intercourse are highest during the
menstrual cycle time from some 5 days before until 1 to 2 days after ovulation. For optimal pregnancy chance, there are recommendations of sexual intercourse every 1 or 2 days, or every 2 or 3 days. Studies have shown no significant difference between different
sex positions
A sex position is a position of the body that people use for sexual intercourse or other sexual activities. Sexual acts are generally described by the positions the participants adopt in order to perform those acts. Though sexual intercourse ge ...
and pregnancy rate, as long as it results in
ejaculation
Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential compone ...
into the
vagina
In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
.
Alternative methods
As an alternative to natural sexual intercourse, there exists
artificial insemination
Artificial insemination is the deliberate introduction of sperm into a female's cervix or uterine cavity for the purpose of achieving a pregnancy through in vivo fertilization by means other than sexual intercourse. It is a fertility treatment ...
, where sperm is introduced into the female reproductive system without the insertion of the penis.
There are also many methods of
assisted reproductive technology, such as
in vitro fertilization
In vitro fertilisation (IVF) is a process of fertilisation where an egg is combined with sperm in vitro ("in glass"). The process involves monitoring and stimulating an individual's ovulatory process, removing an ovum or ova (egg or eggs) f ...
, where one or more
egg cells
The egg cell, or ovum (plural ova), is the female reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete is ...
are retrieved from a woman's ovaries and co-incubated with sperm outside the body. The resulting embryo can then be reinserted into the womb of the woman.
Pregnancy
Pregnancy is the period of time during which the fetus develops, dividing via
mitosis inside the uterus. During this time, the fetus receives all of its
nutrition
Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It provides organisms with nutrients, which can be metabolized to create energy and chemical structures. Failure to obtain sufficient ...
and oxygenated blood from the mother, filtered through the
placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...
, which is attached to the fetus'
abdomen
The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the to ...
via an
umbilical cord
In placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologi ...
. This drain of
nutrients
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excre ...
can be quite taxing on the mother, who is required to ingest slightly higher levels of
calories
The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of o ...
. In addition, certain
vitamins
A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an essential micronutrient that an organism needs in small quantities for the proper functioning of its metabolism. Essential nutrien ...
and other nutrients are required in greater quantities than normal, often creating abnormal eating habits. Gestation period is about 266 days in humans. While in the uterus, the baby first endures a very brief zygote stage, then the embryonic stage, which is marked by the development of major organs and lasts for approximately eight weeks, then the fetal stage, which revolves around the development of bone cells while the fetus continues to grow in size. It is estimated that about 3-5% of couples are infertile and the fecunditity of couples is around 30% for each menstrual cycle.
Labor and birth
Labor is separated into 4 stages. The first stage involves latent phase and active phase separated by the dilation of the cervix for 6 to 10 cm. The second stage is the pushing stage. The third stage involves the delivery of the placenta. And the last stage is the contraction of the uterus.
Once the fetus is sufficiently developed, chemical signals begin the process of birth, which begins with the fetus being pushed out of the birthing canal. The newborn, which is called an
infant in humans, should typically begin
respiration
Respiration may refer to:
Biology
* Cellular respiration, the process in which nutrients are converted into useful energy in a cell
** Anaerobic respiration, cellular respiration without oxygen
** Maintenance respiration, the amount of cellul ...
on its own shortly after birth. Not long after, the placenta eventually falls off on its own. The person assisting the birth may also sever the umbilical cord.
Discovery of mechanism
While most ancient human societies believed that
sexual intercourse was necessary for reproduction, the reasons some sex did not result in children, and the mechanism by which mating produced children were not understood. The theory of
preformationism
In the history of biology, preformationism (or preformism) is a formerly popular theory that organisms develop from miniature versions of themselves. Instead of assembly from parts, preformationists believed that the form of living things exist, ...
was popular in
Ancient Greece
Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean Sea, Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of Classical Antiquity, classical antiquity ( AD 600), th ...
and
Christendom
Christendom historically refers to the Christian states, Christian-majority countries and the countries in which Christianity dominates, prevails,SeMerriam-Webster.com : dictionary, "Christendom"/ref> or is culturally or historically intertwine ...
for centuries. Because they are too small to see with the naked eye, it was only after his invention of the microscope that
Antonie van Leeuwenhoek discovered
spermatozoa
A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromos ...
in 1677.
Mitosis and
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately r ...
were not discovered until the late 1800s.
See also
*
Heterosexuality
*
Antinatalism
Antinatalism or anti-natalism is the view that procreation is wrong. Antinatalists argue that humans should abstain from procreation because it is morally wrong. In scholarly and literary writings, various ethical arguments have been put forth ...
*
Evolution of sexual reproduction
Sexual reproduction is an adaptive feature which is common to almost all multicellular organisms and various unicellular organisms, with some organisms being incapable of asexual reproduction. Currently the adaptive advantage of sexual reprod ...
*
Female infertility
Female infertility refers to infertility in women. It affects an estimated 48 million women, with the highest prevalence of infertility affecting women in South Asia, Sub-Saharan Africa, North Africa/Middle East, and Central/Eastern Europe and Cen ...
*''
Human Reproduction (journal)
''Human Reproduction'' is a peer-reviewed scientific journal covering all aspects of human reproduction, including reproductive physiology and pathology, endocrinology, andrology, gonad function, gametogenesis, fertilization, embryo development, ...
''
*''
Journal of Human Reproductive Sciences
The ''Journal of Human Reproductive Sciences'' is a Peer review, peer-reviewed Open access (publishing), open-access healthcare journal, medical journal published on behalf of the Indian Society of Assisted Reproduction. The journal publishes arti ...
''
*
Male infertility
*
Natalism
*
Paternal age effect
The paternal age effect is the statistical relationship between the father's age at conception and biological effects on the child. Such effects can relate to birthweight, congenital disorders, life expectancy and psychological outcomes. A 2017 ...
*
Reproduction
*
Reproductive system
The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are als ...
*
Legislation on human reproduction
*
Reproductive health
Sexual and reproductive health (SRH) is a field of research, healthcare, and social activism that explores the health of an individual's reproductive system and sexual wellbeing during all stages of their life.
The term can also be further de ...
References
Altrui - The Human Egg Cell Explained
Further reading
* Hopwood, Nick, Rebecca Flemming, Lauren Kassell, eds. ''Reproduction: Antiquity to the Present Day'' (Cambridge UP, 2018). Illustrations. xxxv + 730 pp.
excerptals
online review44 scholarly essays by historians.
*
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